Formable and settable polymer bone composite and method of production thereof

ABSTRACT

A composite osteoimplant. The osteoimplant includes a polymer and bone-derived particles. The composite is adapted and constructed to be formable during or immediately prior to implantation and to be set after final surgical placement.

This application claims the priority of U.S. Provisional Application No.60/432,968, filed Dec. 12, 2002.

FIELD OF THE INVENTION

This invention pertains to a polymer-bone composite, and moreparticularly, to a composite that can be formed in situ or immediatelyprior to implantation.

BACKGROUND OF THE INVENTION

Bone is a composite material composed of impure hydroxyapatite,collagen, and a variety of noncollagenous proteins, as well as embeddedand adherent cells. Bone can be processed into an implantable material,such as an allograft, for example, by treating it to remove the cells,leaving behind the extracellular matrix. The processed bone biomaterialcan have a variety of properties, depending upon the specific processesand treatments applied to it, and may be combined with otherbiomaterials to form a composite that incorporates characteristics ofboth bone and the other biomaterials. For example, bone-derivedmaterials may be processed into load-bearing mineralized grafts thatsupport and integrate with the patient's bone or may alternatively beprocessed into soft, moldable or flowable demineralized bonebiomaterials that have the ability to induce a cellular healingresponse.

The use of bone grafts and bone substitute materials in orthopedicmedicine is well known. While bone wounds can regenerate without theformation of scar tissue, fractures and other orthopedic injuries take asubstantial time to heal, during which the bone is unable to supportphysiologic loads. Metal pins, screws, and meshes are frequentlyrequired to replace the mechanical functions of injured bone. However,metal is significantly stiffer than bone. Use of metal implants mayresult in decreased bone density around the implant site due to stressshielding. Furthermore, some metal implants are permanent and unable toparticipate in physiological remodeling.

Bone's cellular healing processes, using bone tissue formation byostoblast cells coordinated with bone and graft resorption by osteoclastcells, permit bone grafts and certain bone substitute materials toremodel into endogenous bone that is almost indistinguishable from theoriginal. However, the use of bone grafts is limited by the availableshape and size of grafts and the desire to optimize both mechanicalstrength and degradation rate. Variations in bone size and shape amongpatients (and donors) also make bone grafts a less optimal substitutematerial. Bone substitute materials and bone chips are quickly remodeledbut cannot immediately provide mechanical support. In contrast, corticalbone grafts can support physiological stresses but remodel slowly.

Thus, it is desirable to have a bone substitute material for structuralgrafts that may be produced in larger quantities than grafts derivedsolely from bone and that may be fabricated into shapes without beinglimited by the shape of the originating tissue.

Additionally, it is desirable to have a bone substitute material thatmay be adapted to a desired shape during implantation.

SUMMARY OF THE INVENTION

The invention combines the advantages of a formable and a solid implant.The composite can bear weight and other mechanical loads immediatelyafter setting in its rigid state. During implantation, the composite isable to infiltrate and mechanically interlock with porous structuresdisposed about the implant site. The formable composite can be molded orformed to conform to adjacent anatomical and surgical structures (e.g.,other struts, plates, and implants used during surgery) but remainsanchored at the implant site in its rigid state, without unwanteddeformation or motion. After the composite is implanted and hardened, itmay be machined to further conform the surface of the implant to thesurface of the surrounding tissue or to facilitate insertion ofadditional implants or devices. In addition, the composite may beirrigated with saline, water, or other appropriate liquids before,during, or after implantation without displacing, changing the shape of,or otherwise adversely modifying the final implant.

In one aspect, the invention is a composite osteoimplant including apolymer and bone-derived particles. The composite is adapted andconstructed to be formable during or immediately prior to implantationand to be set under predetermined conditions. The composite may beformable at room temperature. Alternatively, the composite may becomeformable when heated to a temperature greater than about 40° C. but notbe as formable at about 37° C. For example, the composite may becomeformable when heated to a temperature greater than about 45° C., 50° C.,55° C., 60° C., 70° C., 80° C., or 90° C. The composite may become moreset by increasing the cross-link density of the polymer component. Thecomposite may further include a monomer and become set when the monomeris covalently incorporated into the polymer.

The composite may further include one or more of bone marrow, abiomolecule, a small molecule, a bioactive agent, calcium phosphate,calcium carbonate, and cells. For example, the composite may include oneor more of a nucleic acid vector, mesenchymal stem cells, osteoblasts,osteoclasts, and fibroblasts. The nucleic acid vector, when introducedinto a cell, may increase the cell's production of bone morphogeneticproteins. The osteoimplant may be adapted and constructed to beirrigated following implantation without substantially changing itsshape. The bone-derived particles may be about 10% to about 99% byweight of the composite, for example, about 25% to about 50%.

A surface of the bone-derived particles may be modified with one or moreof a biomolecule, a small molecule, a bioactive agent, and anon-biologically active material. Collagen fibers at the surface of thebone-derived particles may be exposed and may optionally be partially orfully separated from one another. The exposed collagen fibers may bederivatized with one or more of a biomolecule, a small molecule, abioactive agent, and a non-biologically active material. The polymer maybe biodegradable or non-biodegradable and may be a mixture or co-polymerof biodegradable polymers, non-biodegradable polymers, or both.

The osteoimplant may include a plurality of pieces of composite that arejoined together, for example, with one or more of an adhesive, amechanical fastener, and ultrasonic bonding. The composite may beadapted and constructed to be formed in a mold.

The distribution of bone particles within the composite may vary withinthe composite with respect to one or more of volume fraction, size,density, size distribution, and shape. At least a portion of thebone-derived particles in the composite may be elongate, and thearrangement of particles within the composite may be isotropic oranisotropic. The relative alignment of elongate bone-derived particlesin the composite may be different in a first portion, a second portion,and/or subsequent portions of the composite. The bone-derived particlesand the polymer may be linked with a silane coupling agent. In anotheraspect, the invention is a method of preparing an osteoimplant. Themethod includes the steps of forming a composite comprising bone-derivedparticles and a polymer into a predetermined shape and causing thepolymer to set. The method may further include combining the compositewith autogenous tissue, including autograft bone.

The predetermined shape may be that of a wound site in a bone and thestep of forming may include packing the wound site with the composite.Before the composite is formed into a shape, it may be heated to atemperature at which it is formable, and the polymer may be set byallowing it to cool to ambient temperature or body temperature.Alternatively, the polymer may be set by increasing the cross-linkdensity of the polymer. The osteoimplant may further include amechanical fastener, and the composite may be formed so as to retain themechanical fastener after the polymer is set.

In another embodiment, the invention is a kit for producing anosteoimplant. The kit includes a polymer adapted and constructed to beformable under predetermined conditions and set after final surgicalplacement of the osteoimplant and bone-derived particles. Under thepredetermined conditions, the polymer and the bone-derived particles maybe combined and formed into a predetermined shape. The predeterminedconditions may include a temperature greater than about 40° C. Thepolymer may be set by exposing it to an energy source for apredetermined period of time. The osteoimplant may be adapted andconstructed to be irrigated following implantation without substantiallychanging its shape. The predetermined shape may be defined by a mold.The composite may be adapted and constructed to be implanted by formingit within a tissue site.

In another aspect, the invention is a method of producing a compositefor use in an osteoimplant. The method comprises providing a polymeradapted and constructed to be formable under a first predeterminedcondition and set under a second predetermined condition, providing aplurality of bone-derived particles, and combining the polymer and theplurality of bone-derived particles under the first predeterminedcondition. The polymer and the plurality of bone-derived particles mayfurther be combined with autogenous tissue. Before the step ofcombining, the polymer may be heated to a temperature at which it isformable. After combining, the composite may be allowed to cool toambient or body temperature. A mechanical fastener may be incorporatedinto the composite.

The method may further include forming a second composite and causing itto set, following which the two composites are joined together to forman osteoimplant. The method may further include machining the compositeinto a shape before or after the step of forming, or any combination ofthese.

The method may further include combining bone-derived particles and apolymer to produce the composite. The particles and the polymer may becombined by pressing a mixture of polymer and bone-derived particles,hand mixing bone-derived particles into formable polymer, heating thepolymer, solvent casting a polymer and bone-derived particles, injectionmolding, extrusion forming, pressing a coating of bone-derived particlesinto a sheet of polymer, and combining the polymer with a solvent. Thecomposite may be formed by making a shape from the composite in a moldor arranging the composite in a tissue site.

The composite may be adapted to be formable into a shape of a wound sitein a bone or to be shaped in a mold. The method may further compriseproducing a second composite and joining the composites together to forman osteoimplant, for example, with one or more of an adhesive, amechanical fastener, and ultrasonic bonding.

The composite may be adapted and constructed to be formed into a shapein a mold or a tissue site under the predetermined conditions. Thecomposite may become set because the cross-link density of the polymeris increased. A monomer may be combined with the plurality of boneparticles and the polymer, and the composite may become set when themonomer is incorporated into the polymer. The composite may become setwhen the polymer is brought to a temperature less than a temperature atwhich the polymer is formable.

Definitions

“Anisotropic”: The term “anisotropic,” as used herein, describes acharacteristic of a material that varies with the axis of measurement.

“Biomolecules”: The term “biomolecules,” as used herein, refers toclasses of molecules (e.g., proteins, amino acids, peptides,polynucleotides, nucleotides, carbohydrates, sugars, lipids,nucleoproteins, glycoproteins, lipoproteins, steroids, etc.) that arecommonly found in cells and tissues, whether the molecules themselvesare naturally-occurring or artificially created (e.g., by synthetic orrecombinant methods). For example, biomolecules include, but are notlimited to, enzymes, receptors, neurotransmitters, hormones, cytokines,cell response modifiers such as growth factors and chemotactic factors,antibodies, vaccines, haptens, toxins, interferons, ribozymes,anti-sense agents, plasmids, DNA, and RNA.

“Biocompatible”: The term “biocompatible,” as used herein is intended todescribe materials that, upon administration in vivo, do not induceundesirable long term effects.

“Biodegradable”: As used herein, “biodegradable” materials are materialsthat degrade under physiological conditions to form a product that canbe metabolized or excreted without damage to organs. Biodegradablematerials are not necessarily hydrolytically degradable and may requireenzymatic action to fully degrade. Biodegradable materials also includematerials that are broken down within cells.

“Composite”: As used herein, the term “composite” is used to refer to aunified combination of two or more distinct materials.

“Formable”: As used herein, “formable” materials are those that can beshaped by mechanical deformation. Exemplary methods of deformationinclude, without limitation, injection molding, extrusion, pressing,casting, rolling, and molding. In one embodiment, formable materials maybe shaped by hand or using hand-held tools, much as an artistmanipulates clay.

“Glass Transition Temperature”: As used herein, the term “glasstransition temperature” (T_(g)) indicates the lowest temperature atwhich an amorphous or partially amorphous polymer is considered softenedand possibly flowable. As referred to herein, the value of T_(g) is tobe determined using differential calorimetry as per ASTM StandardE1356-98 “Standard Test Method for Assignment of the Glass TransitionTemperatures by Differential Scanning Calorimetry or DifferentialThermal Analysis.”

“Isotropic”: As used herein, the term “isotropic” is used to describe acharacteristic of a material that does not vary with the axis ofmeasurement.

“Melting Temperature”: As used herein, the term “melting temperature”(T_(m)) is defined as the temperature, at atmospheric pressure, at whicha polymer changes its state from solid to liquid. As referred to herein,the value of T_(m) is the value of T_(pm1) as determined according toper ASTM Standard D3418-99 “Standard Test Method for TransitionTemperatures of Polymers By Differential Scanning Calorimetry.”

“Osteoinductive”: As used herein, the term “osteoinductive” is used torefer to the ability of a substance to recruit cells from the host thathave the potential for forming new bone and repairing bone tissue. Mostosteoinductive materials can stimulate the formation of ectopic bone insoft tissue.

“Osteoconductive”: As used herein, the term “osteoconductive” is used torefer to the ability of a non-osteoinductive substance to serve as asuitable template or substrate along which bone may grow.

“Osteoimplant”: As used herein, the term “osteoimplant” does not implythat the implant contains a specific percentage of bone or has aparticular shape, size, configuration or application.

“Polynucleotide,” “nucleic acid,” or “oligonucleotide”: The terms“polynucleotide,” “nucleic acid,” or “oligonucleotide” refer to apolymer of nucleotides. The terms “polynucleotide”, “nucleic acid”, and“oligonucleotide”, may be used interchangeably. Typically, apolynucleotide comprises at least three nucleotides. DNAs and RNAs arepolynucleotides. The polymer may include natural nucleosides (i.e.,adenosine, thymidine, guanosine, cytidine, uridine, deoxyadenosine,deoxythymidine, deoxyguanosine, and deoxycytidine), nucleoside analogs(e.g., 2-aminoadenosine, 2-thiothymidine, inosine, pyrrolo-pyrimidine,3-methyl adenosine, C5-propynylcytidine, C5-propynyluridine,C5-bromouridine, C5-fluorouridine, C5-iodouridine, C5-methylcytidine,7-deazaadenosine, 7-deazaguanosine, 8-oxoadenosine, 8-oxoguanosine,O(6)-methylguanine, and 2-thiocytidine), chemically modified bases,biologically modified bases (e.g., methylated bases), intercalatedbases, modified sugars (e.g., 2′-fluororibose, ribose, 2′-deoxyribose,arabinose, and hexose), or modified phosphate groups (e.g.,phosphorothioates and 5′-N-phosphoramidite linkages).

“Polypeptide”, “peptide”, or “protein”: According to the presentinvention, a “polypeptide,” “peptide,” or “protein” comprises a stringof at least three amino acids linked together by peptide bonds. Theterms “polypeptide”, “peptide”, and “protein”, may be usedinterchangeably. Peptide may refer to an individual peptide or acollection of peptides. Inventive peptides preferably contain onlynatural amino acids, although non-natural amino acids (i.e., compoundsthat do not occur in nature but that can be incorporated into apolypeptide chain; see, for example,http://www.cco.caltech.edu/˜dadgrp/Unnatstruct.gif, which displaysstructures of non-natural amino acids that have been successfullyincorporated into functional ion channels) and/or amino acid analogs asare known in the art may alternatively be employed. Also, one or more ofthe amino acids in an inventive peptide may be modified, for example, bythe addition of a chemical entity such as a carbohydrate group, aphosphate group, a farnesyl group, an isofarnesyl group, a fatty acidgroup, a linker for conjugation, functionalization, or othermodification, etc. In a preferred embodiment, the modifications of thepeptide lead to a more stable peptide (e.g., greater half-life in vivo).These modifications may include cyclization of the peptide, theincorporation of D-amino acids, etc. None of the modifications shouldsubstantially interfere with the desired biological activity of thepeptide.

“Polysaccharide”, “carbohydrate” or “oligosaccharide”: The terms“polysaccharide,” “carbohydrate,” or “oligosaccharide” refer to apolymer of sugars. The terms “polysaccharide”, “carbohydrate”, and“oligosaccharide”, may be used interchangeably. Typically, apolysaccharide comprises at least three sugars. The polymer may includenatural sugars (e.g., glucose, fructose, galactose, mannose, arabinose,ribose, and xylose) and/or modified sugars (e.g., 2′-fluororibose,2′-deoxyribose, and hexose).

“Settable”: As used herein, the term “settable” refers to a materialthat may be rendered more resistant to mechanical deformation withrespect to a formable state.

“Set”: As used herein, the term “set” refers to the state of a materialthat has been rendered more resistant to mechanical deformation withrespect to a formable state.

“Small molecule”: As used herein, the term “small molecule” is used torefer to molecules, whether naturally-occurring or artificially created(e.g., via chemical synthesis), that have a relatively low molecularweight. Typically, small molecules have a molecular weight of less thanabout 5000 g/mol. Preferred small molecules are biologically active inthat they produce a local or systemic effect in animals, preferablymammals, more preferably humans. In certain preferred embodiments, thesmall molecule is a drug. Preferably, though not necessarily, the drugis one that has already been deemed safe and effective for use by theappropriate governmental agency or body. For example, drugs for humanuse listed by the FDA under 21 C.F.R. §§ 330.5, 331 through 361, and 440through 460; drugs for veterinary use listed by the FDA under 21 C.F.R.§§ 500 through 589, incorporated herein by reference, are all consideredacceptable for use in accordance with the present invention.

“Bioactive agents”: As used herein, the term “bioactive agents” is usedto refer to compounds or entities that alter, inhibit, activate, orotherwise affect biological or chemical events. For example, bioactiveagents may include, but are not limited to, anti-AIDS substances,anti-cancer substances, antibiotics, immunosuppressants, anti-viralsubstances, enzyme inhibitors, neurotoxins, opioids, hypnotics,anti-histamines, lubricants, tranquilizers, anti-convulsants, musclerelaxants and anti-Parkinson substances, anti-spasmodics and musclecontractants including channel blockers, miotics and anti-cholinergics,anti-glaucoma compounds, anti-parasite and/or anti-protozoal compounds,modulators of cell-extracellular matrix interactions including cellgrowth inhibitors and anti-adhesion molecules, vasodilating agents,inhibitors of DNA, RNA or protein synthesis, anti-hypertensives,analgesics, anti-pyretics, steroidal and non-steroidal anti-inflammatoryagents, anti-angiogenic factors, anti-secretory factors, anticoagulantsand/or antithrombotic agents, local anesthetics, ophthalmics,prostaglandins, anti-depressants, anti-psychotic substances,anti-emetics, and imaging agents. In a certain preferred embodiments,the bioactive agent is a drug.

A more complete listing of bioactive agents and specific drugs suitablefor use in the present invention may be found in “PharmaceuticalSubstances: Syntheses, Patents, Applications” by Axel Kleemann andJurgen Engel, Thieme Medical Publishing, 1999; the “Merck Index: AnEncyclopedia of Chemicals, Drugs, and Biologicals”, Edited by SusanBudavari et al., CRC Press, 1996; and the United StatesPharmacopeia-25/National Formulary-20, published by the United StatesPharmcopeial Convention, Inc., Rockville Md., 2001, each of which isincorporated herein by reference.

DETAILED DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS

The invention includes providing bone or other fill material and abiocompatible polymer to form a composite. The composite is adapted andconstructed to be formable in a particular condition. For example, thecomposite may be formable after heating to or above a predeterminedtemperature. After forming, the composite is rendered less formable, forexample, by cooling or cross-linking.

The composite may be molded by a surgeon or other skilled operatoreither immediately prior to implantation into a tissue site, duringimplantation into the site, and/or for a period after implantation intothe site. Thus, the surgeon does not have to prepare an implant havingthe exact shape of the tissue site prior to surgery or prepare a sitefor a particular implant configuration. Instead, the implant may beshaped in situ.

Preparation of Bone

The bone particles employed in the preparation of the inventive boneparticle-containing compositions can be obtained from cortical,cancellous and/or corticocancellous bone which may be of autogenous,allogenic, transgenic, and/or xenogeneic origin. Preferably, the boneparticles are obtained from cortical bone of allogenic origin. Porcineand bovine bone are particularly advantageous types of xenogeneic bonetissue which can be used individually or in combination as sources forthe bone particles. Particles are formed by milling whole bone toproduce fibers, chipping whole bone, cutting whole bone, fracturingwhole bone in liquid nitrogen, or otherwise disintegrating the bonetissue. Particles can optionally be sieved to produce particles in aspecific size range.

In one embodiment, the bone particles have a size (i.e., the largestdimension) between about 50 μm and about 1 mm, for example, betweenabout 100 μm and about 1 mm, to optimize ease of manipulation of thecomposite. Both smaller and larger particles may also be used in thecomposites of the invention. For example, bone particles with a largestdimension smaller than about 40 μm, about 30 μm, about 20 μm, or about10 μm may be used. Larger particles, e.g., about 2-3 mm across orgreater, may also be employed. The desired particle size anddistribution will depend in part on the implant site, size, and shape.Large particles will reduce the possible resolution of a desired shape.For example, a composite with large particles may be difficult to forminto a shape having small nooks or other details. The particle size willalso affect the speed with which heat retained in the particles isreleased to the surrounding polymer (see below).

Alternatively or in combination, bone particles generally characterizedas elongate and possessing relatively high median length to medianthickness ratios can be utilized herein. Such elongate particles can bereadily obtained by any one of several methods, e.g., by milling orshaving the surface of an entire bone or relatively large section ofbone. Employing a milling technique, optionally followed by sortingand/or separating by length, diameter, or both, one can obtain elongatebone particles possessing a median length of from about 2 to about 200mm or more, for example, from about 10 to about 100 mm, a medianthickness of from about 0.05 to about 2 mm, for example, from about 0.2to about 1 mm and a median width of from about 1 mm to about 20 mm, forexample, from about 2 to about 5 mm. These elongate bone particles canpossess a median length to median thickness ratio of at least about 50:1up to about 500:1 or more, for example, from about 50:1 to about 100:1,and a median length to median width ratio from about 10:1 to about200:1, for example, from about 50:1 to about 100:1. The milling processmay be optimized to adjust the size of the bone particles and the sizedistribution. The mechanical strength, elastic modulus, and anisotropyof the implant can be tailored by adjusting the weight percent of thevarious shapes (elongate, particlulate, etc.) of bone particles utilizedin the composite. Elongate and more evenly dimensioned particles may beused alone or in mixtures in any ratio between 0% and 100% elongateparticles.

Another procedure for obtaining elongate bone particles, particularlyuseful for pieces of bone of up to about 100 mm in length, is the boneprocessing mill described in commonly assigned U.S. Pat. No. 5,607,269,the contents of which are incorporated herein by reference. Use of thisbone mill results in the production of long, thin strips which quicklycurl lengthwise to provide tubular-like bone particles. If desired,elongate bone particles can be graded into different sizes to reduce oreliminate any less desirable size(s) of particles which may be present.In overall appearance, elongate bone particles can be described asfilaments, fibers, threads, slender or narrow strips, etc.

The bone particles are optionally demineralized in accordance with knownand conventional procedures in order to reduce their inorganic mineralcontent. Demineralization methods remove the inorganic mineral componentof bone by employing acid solutions. Such methods are well known in theart, see for example, Reddi et al., Proc. Nat. Acad Sci (1972) 69:1601-1605, the contents of which are incorporated herein by reference.The strength of the acid solution, the shape of the bone particles andthe duration of the demineralization treatment will determine the extentof demineralization. Reference in this regard may be made toLewandrowski et al., J Biomed Materials Res, (1996) 31: 365-372, andU.S. Pat. No. 5,290,558, the contents of both of which are incorporatedherein by reference.

In a preferred demineralization procedure, the bone particles aresubjected to a defatting/disinfecting step which is followed by an aciddemineralization step. A preferred defatting/disinfectant solution is anaqueous solution of ethanol. Ordinarily, at least about 10 to about 40percent by weight of water (i.e., about 60 to about 90 weight percent ofdefatting agent such as alcohol) should be present in thedefatting/disinfecting solution to remove lipids and disinfect the boneparticles within the shortest period of time. The preferredconcentration range of the defatting solution is from about 60 to about85 weight percent alcohol and most preferably about 70 weight percentalcohol. Following defatting, the bone particles are immersed in acidover time to effect their demineralization. The acid solution alsodisinfects the bone by killing microorganisms and viruses. Acids whichcan be employed in this step include inorganic acids such ashydrochloric acid and organic acids such as peracetic acid. After acidtreatment, the demineralized bone particles are rinsed with sterilewater to remove residual amounts of acid. Where elongate bone particlesare employed, some entanglement of the demineralized bone particles willresult. The demineralized bone particles can then be immediately shapedinto any desired configuration or stored under aseptic conditions,advantageously in a lyophilized state, for processing at a later time.As an alternative to aseptic processing and storage, the particles canbe shaped into a desired configuration and sterilized using suitablemethods known to those skilled in the art.

As used herein, the phrase “superficially demineralized” as applied tothe bone particles refers to bone particles possessing at least about 90weight percent of their original inorganic mineral content. Superficialdemineralization produces particles containing a mineralized core. Thephrase “partially demineralized” as applied to the bone particles refersto bone particles possessing from about 8 to about 90 weight percent oftheir original inorganic mineral content, and the phrase “fullydemineralized” as applied to the bone particles refers to bone particlespossessing less than about 8, preferably less than about 1, weightpercent of their original inorganic mineral content. The unmodified term“demineralized” as applied to the bone particles is intended to coverany one or combination of the foregoing types of demineralized boneparticles.

Mixtures or combinations of one or more of the foregoing types of boneparticles can be employed. For example, one or more of the foregoingtypes of demineralized bone particles can be employed in combinationwith nondemineralized bone particles, i.e., bone particles that have notbeen subjected to a demineralization process. Nondemineralized,non-elongate bone particles will also function much like ceramicinclusions, increasing the compressive strength of the composite.Nondemineralized bone, including nondemineralized portions of partiallydemineralized bone, is itself a fiber-reinforced composite, increasingthe bending and tensile stress the composite can withstand before thebone particles fracture.

The bone particles in the composite also play a biological role.Non-demineralized bone particles bring about new bone ingrowth byosteoconduction. Demineralized bone particles likewise play a biologicalrole in bringing about new bone ingrowth by osteoinduction. Both typesof bone particles are gradually remodeled and replaced by new host boneas degradation of the composite progresses over time.

The differential in strength, osteogenicity and other properties betweenpartially and fully demineralized bone particles on the one hand andnon-demineralized and superficially demineralized bone particles on theother hand can be exploited. For example, nondemineralized and/orsuperficially demineralized bone particles can be concentrated in thatregion of the osteoimplant which will be directly subjected to loadingduring and/or after implantation. In order to increase the compressivestrength of the osteoimplant, the ratio of nondemineralized and/orsuperficially demineralized bone particles to partially or fullydemineralized bone particles may favor the former, and vice versa. Thus,the use of various types of bone particles can be used to control theoverall mechanical and biological properties, i.e., the strength,osteoconductivity and/or osteoinductivity, etc., of the osteoimplant.

The amount of each individual type of bone particle employed can varywidely depending on the mechanical and biological properties desired.Thus, mixtures of bone particles of various shapes, sizes, and/ordegrees of demineralization may be assembled based on the desiredmechanical, thermal, and biological properties of the composite. Inaddition or alternatively, composites may be formed having a single typeof one particle or with multiple sections, each having a different typeor mixture of bone particles. Suitable amounts of particle types can bereadily determined by those skilled in the art on a case-by-case basisby routine experimentation.

If desired, the bone particles can be modified in one or more ways,e.g., their protein content can be augmented or modified as described,for example, in U.S. Pat. Nos. 4,743,259 and 4,902,296, the contents ofboth of which are incorporated herein by reference.

Selection of Polymer

Practically any biocompatible polymer may be used in the composites ofthe invention. Co-polymers and/or polymer blends may also be exploited.The selected polymer preferably should be formable and settable underparticular conditions. For example, the composite may become moreformable when heated to or over a particular temperature, for example, atemperature at or above the glass transition temperature of the polymercomponent. Alternatively, the composite may be more formable when thepolymer component has a certain cross-link density. After the compositeis formed into the desired shape, the cross-link density of the polymercomponent of the composite is increased to render the composite lessformable. In another embodiment, a small amount of monomer is mixed withthe polymeric and bone components of the composite. Upon exposure to anenergy source, e.g., UV light, the monomer and polymer will furtherpolymerize, increasing the molecular weight, the cross-link density, orboth.

If heat is employed to render the composite and/or the polymer componentof the composite formable, the glass transition or melting temperatureof the polymer component is preferably higher than normal bodytemperature, for example, higher than 40° C. Polymers that become moreformable at higher temperatures, e.g., higher than 45°, 50°, or 55°, mayalso be used. Exemplary polymers having T_(g) suitable for use with theinvention include but are not limited to starch poly(caprolactone),poly(caprolactone), poly(l-lactide), poly(dl-lactide-co-glycolide),poly(l-lactide-co-dl-lactide), and co-polymers, mixtures, andenantiomers thereof.

It is not necessary for all embodiments that the glass transitiontemperature of the polymer be higher than body temperature. In non-loadbearing and some load-bearing applications, the viscosity of the polymerneed only be high enough that the composite will not flow out of theimplant site. In other embodiments, the polymer component may havecrystalline and non-crystalline regions. Depending on the ratio ofcrystalline and non-crystalline material, the polymer component mayremain relatively rigid between the glass transition and meltingtemperatures. Indeed, for some polymers, the melting temperature willdetermine when the polymer component becomes formable.

Since the composite may be rendered formable just prior to implantation,polymer components with glass transition or melting temperatures higherthan 60° C. are also suitable for use with the invention, despite thesensitivity of biological material to heat.

Potential damage to bone and/or other materials in the composite dependson both the temperature and the processing time. As the T_(g) or T_(m)of the polymer component increases, the composite should be heated forshorter periods of time to minimize damage to its biological components.

The T_(g) of a polymer may be manipulated by adjusting its cross-linkdensity and its molecular weight. Thus, for polymers whose glasstransition temperatures are not sufficiently high, increasing thecross-link density or molecular weight can increase the T_(g) to a levelat which composites containing these polymers can be heated to renderthem formable. Alternatively, the polymer may be produced withcrystalline domains, increasing the stiffness of the polymer attemperatures above its glass transition temperature. In addition, theT_(g) of the polymer component may be modified by adjusting thepercentage of the crystalline component. Increasing the volume fractionof the crystalline domains may so reduce the formability of the polymerbetween T_(g) and T_(m) that the composite has to be heated above itsmelting point to be sufficiently formable for use with the invention.

Any biocompatible polymer may be used to form composites according tothe invention. As noted above, the cross-link density and molecularweight of the polymer may need to be manipulated so that the polymer maybe formed and set when desired. A number of biodegradable andnon-biodegradable biocompatible polymers are known in the field ofpolymeric biomaterials, controlled drug release and tissue engineering(see, for example, U.S. Pat. Nos. 5,804,178; 5,770,417; 5,736,372;5,716,404 to Vacanti; U.S. Pat. Nos. 6,095,148; 5,837,752 to Shastri;U.S. Pat. No. 5,902,599 to Anseth; U.S. Pat. Nos. 5,696,175; 5,514,378;5,512,600 to Mikos; U.S. Pat. No. 5,399,665 to Barrera; U.S. Pat. No.5,019,379 to Domb; U.S. Pat. No. 5,010,167 to Ron; U.S. Pat. No.4,946,929 to d'Amore; and U.S. Pat. Nos. 4,806,621; 4,638,045 to Kohn;see also Langer, Acc. Chem. Res. 33:94, 2000; Langer, J. Control Release62:7, 1999; and Uhrich et al., Chem. Rev. 99:3181, 1999, the contents ofall of which are incorporated herein by reference).

Preferably, the polymer matrix is biodegradable. Exemplary biodegradablematerials, in addition to those listed above, include but are notlimited to poly(arylates), poly(anhydrides), poly(hydroxy acids),polyesters, poly(ortho esters), polycarbonates, poly(propylenefumerates), poly(amide esters), poly (amide carbonates), polyamides,polyamino acids, polyacetals, polylactides, polyglycolides,poly(dioxanones), polyhydroxybutyrate, polyhydroxyvalyrate, poly(vinylpyrrolidone), biodegradable polycyanoacrylates, biodegradablepolyurethanes, polyalkylene oxides, polymino carbonates, polyesteramides, polyester imides, amino acid polyarylates, amino acidpolycarbonates, and polysaccharides. Tyrosine-based polymers, includingbut not limited to polyarylates and polycarbonates, may also be employed(see Pulapura, et al., “Tyrosine-derived polycarbonates:Backbone-modified “pseudo”-poly(amino acids) designed for biomedicalapplications,” Biopolymers, 1992, 32: 411-417; Hooper, et al.,“Diphenolic monomers derived from the natural amino acid α-L-tyrosine:an evaluation of peptide coupling techniques,” J. Bioactive andCompatible Polymers, 1995, 10:327-340, the contents of both of which areincorporated herein by reference).

Non-biodegradable polymers may also be used as well. For example,polypyrrole, polyanilines, polythiophene, and derivatives thereof areuseful electroactive polymers that can transmit voltage from theendogenous bone to an implant. Other non-biodegradable, yetbiocompatible polymers include polystyrene, non-biodegradablepolyurethanes, polyureas, poly(ethylene vinyl acetate), polypropylene,polymethacrylate, polyethylene, and poly(ethylene oxide).

These polymers and the monomers that are used to produce any of thesepolymers are easily purchased from companies such as Polysciences,Sigma, and Scientific Polymer Products. Those skilled in the art willrecognize that this is an exemplary, not a comprehensive, list ofpolymers appropriate for in vivo applications. Co-polymers, adducts,and/or blends of any of the polymers discussed herein may also be usedin the practice of the invention.

In another embodiment, the composite is produced with a formable polymerand then hardened in situ. For example, the cross-link density of apolymer may be increased by exposing it to UV light or an alternativeenergy source. Alternatively, a photoactive cross-linking agent,chemical cross-linking agent, additional monomer, or combinationsthereof may be mixed into the composite. Exposure to UV light after thecomposite is fitted to the implant site will increase one or both of themolecular weight and cross-link density, stiffening the polymer. Thepolymer component of the composite may also be softened by a solvent,e.g., ethanol. If a biocompatible solvent is used, the polymer may behardened in situ or ex situ, for example, after molding. As thecomposite hardens, solvent leaving the composite material should bereleased into the surrounding tissue without causing undesirable effectssuch as irritation. If a non-biocompatible solvent is used, standardtechniques such as vacuum, weight measurements, and chemical samplingmay be used to determine whether sufficient amounts of the solvent hasbeen removed from the composite before implantation in a patient.

Combining the Polymer and Bone

The polymer and the bone may be combined by any method known to thoseskilled in the art. For example, a homogenous mixture of polymer andbone particles may be pressed together at ambient or elevatedtemperatures. The pressed composite will maintain its shape and relativeparticle positioning. At elevated temperatures, the process may also beaccomplished without pressure. Preferably, the polymer is not held at atemperature of greater than 80° C. for a significant time during mixingto prevent thermal damage to the biological component of the composite.Bone particles may be incorporated into a formable polymer by a varietyof methods. For example, bone particles may also be mixed or folded intoa polymer softened by heat or a solvent. Alternatively, a formablepolymer may be formed into a sheet that is then covered with a layer ofbone particles. The bone may then be forced into the polymer sheet usingpressure. In another embodiment, bone particles are individually coatedwith polymer, for example, using a tumbler, spray coater, or a fluidizedbed, before being mixed with a larger quantity of polymer. Thisfacilitates even coating of the bone particles and improves integrationof the bone particles and polymer.

Polymer processing techniques may also be used to combine the boneparticles and polymer. For example, the polymer may be renderedformable, e.g., by heating or with a solvent, and combined with the boneparticles by injection molding or extrusion forming. Alternatively, thepolymer and bone particles may be mixed in a solvent and cast with orwithout pressure. The composite may be prepared from both formable andrigid polymers. For example, extrusion forming may be performed usingpressure to manipulate a formable or rigid polymer. Once the compositeis mixed, it may be desirable to store it in a container that imparts astatic pressure to prevent separation of the bone particles and thepolymer, which have different densities.

Alternatively, the polymer and bone may be supplied separately, e.g., ina kit, and mixed immediately prior to implantation or molding. The kitmay contain a preset supply of bone-derived particles having certainsizes, shapes, and levels of demineralization. The surface of thebone-derived particles may have been modified using one or more of thetechniques described herein. Alternatively, the kit may provide severaldifferent types of bone-derived particles of varying sizes, shapes, andlevels of demineralization, and that may have been chemically modifiedin different ways. A surgeon or other professional may also combine thecomponents in the kit with autologous tissue derived during surgery. Forexample, the surgeon may want to include autogenous tisue, e.g., bonemarrow or bone shavings generated while preparing the implant site, intothe composite.

These techniques may be used to prepare composites having a wide varietyof configurations. For example, while most composites will employ ahomogenous mixture of polymer and bone, it may be desirable to form acomposite in which the bone is more highly concentrated on an exterioror an interior portion of the material. In addition, the composite neednot be isotropic. Composites may be formed having different boneparticle sizes, shapes, or volume fractions in different portions of thecomposite. For example, a composite may be formed having largerparticles in an exterior portion and smaller particles in an interiorportion, or vice versa. The composite may be formed with a gradient ofparticle types, sizes, size distributions, shapes, densities, or volumefractions. The distribution of particles may be centrosymmetric, mayreflect some other symmetry, or may be asymmetric. If the composite isformed in sections, e.g., having different arrangements, densities,volume fractions, etc. of particles, various polymer joining techniques,for example, adhesives or mechanical fasteners, may be used to unite thesections into a single implant. For example, ultrasonic welding willenable the polymer at the boundaries between the sections to blend withthe particles without significantly disturbing the arrangement of theparticles.

Elongated particles may be distributed in the polymer in a variety ofarrangements. For example, elongated particles may be aligned in aparticular direction throughout the composite. Alternatively, thecomposite may be assembled in layers and the orientation of the elongateparticles rotated by some angle, e.g. 90° or 45°, in each layer. Smallerangles may be used to form a helical pattern. Alternatively or inaddition, elongated bone particles may be used in one portion of thecomposite while more regularly dimensioned particles are used inanother.

To align elongated particles, the composite may be rolled, extruded,twisted, or otherwise mechanically aligned. Alternatively, the elongatedparticles may be deposited into the polymer as they are produced. Forexample, grated or milled bone particles tend to exit the millingapparatus roughly aligned with one another. Instead of being collected,the particles may be delivered directly from the mill to the softenedpolymer, onto which they will fall in roughly the same orientation, muchlike cheese passing through a plane grater. A static electric chargeimparted to the bone particles can also facilitate alignment. Frictiongenerated during milling (if the apparatus is not water-coated) orsieving may be sufficient to cause alignment. Alternatively, an electricfield may be created across a sieve to impart added charge. Producingrandomly oriented particles requires other techniques. Mechanicalstirring usually produces areas of local alignment. Bubbling may imparta slight upwards orientation but otherwise can effectively randomize theorientation of the particles. Agitation may also be an effective processto randomize orientation.

The composite may include practically any ratio of polymer and bone, forexample, between about 5 weight % polymer and about 90 weight % polymer.For example, the composite may include about 25% to about 30% polymer orapproximately equal weights of polymer and bone. The proportions of thepolymer and bone can influence various characteristics of the composite,for example, its mechanical properties, including fatigue, and thedegradation rate. In addition, the cellular response to the compositewill vary with the proportion of polymer and bone. One skilled in theart will recognize that standard experimental techniques may be used totest these properties for a range of compositions to optimize acomposite for a desired application. For example, standard mechanicaltesting instruments may be used to test the compressive strength andstiffness of the composite.

Cells may be cultured on the composite for an appropriate period of timeand the metabolic products and the amount of proliferation (e.g., thenumber of cells in comparison to the number of cells seeded) analyzed.The weight change of the composite may be measured after incubation insaline or other fluids. Repeated analysis will demonstrate whetherdegradation is linear or not, and mechanical testing of the incubatedmaterial will show the change in mechanical properties as the compositedegrades. Such testing may also be used to compare the enzymatic andnon-enzymatic degradation of the composite and to determine the levelsof enzymatic degradation.

Mechanical Considerations

In a preferred embodiment, the bone particles in the composite, ratherthan the polymer matrix, carry the majority of the applied load, whilethe polymer matrix holds the particles in place. For example, largerpieces of bone may be stacked on top of one another in a pre-form andpolymer allowed to flow around the bone pieces, following which thepolymer is allowed to set. The polymer component of the composite may berendered formable to implant the composite into a tissue site. Forexample, a surgeon can manipulate a composite within a formablecomponent to fit a specific patient site during surgery. This allowsstructural implants of a desired shape to be produced from irregularlyshaped pieces of bone. Cortical bone has relatively high compressivestrength; however, the forces exerted at the polymer-filled boundariesbetween bone pieces will have a shear component.

In an alternative embodiment, the surfaces of the bone particles aredemineralized, following which the exposed collagen of adjacent boneparticles is cross-linked using the techniques of our commonly ownedU.S. Pat. No. 6,123,731, entitled Osteoimplant and Method for itsManufacture, the contents of which are incorporated herein by reference.Exemplary cross-linking methods include chemical reaction, irradiation,application of heat, dehydrothermal treatment, enzymatic treatment, etc.Alternatively or in addition, where bone particles having varyingdegrees of demineralization are used, bone particles may be bonded toone another by linking exposed collagen of demineralized particles tothe inorganic component of non-demineralized bone particles usingcoupling agents, for example, silane coupling agents. In a furtherembodiment, the mineral content of the particle surfaces may be enhancedby rinsing with phosphoric acid, e.g., 1 to 15 minutes in a 5-50%solution by volume. Alternatively, bone particles may be treated toinduce deposition of one or more of hydroxyapatite, tricalciumphosphate, polycrystalline calcium, calcium carbonate, corallinecalcium, calcium phosphate, calcium hydrogen phosphate, calciumphosphosilicate, tetrabasic calcium phosphate, sodium chondroitinsulfate, sodium succinate anhydride, calcium sulfate, magnesiumstearate, calcium sulfate dihydrate, polyvinyl pyrrolidone, propyleneglycol-co-fumaric acid, calcified polyurethane,baria-boroalumino-silicate glass, and/or polylactide-co-glycolidedeposition and crystal formation on exposed collagen fibers. The polymerwill form around these fibers, increasing interfacial area and improvingthe wet strength of the composite.

Additional Components

Additional materials may be included in the composite. Autologoustissues such as bone marrow and bone particles may be combined with thealready mixed composite or mixed with polymer and bone particles from akit to form the composite immediately before implantation. The compositemay include additional calcium-based ceramics such as calcium phosphateand calcium carbonate. Non-biologically active materials may also beincorporated into the composite. For example, radiopaque, luminescent,or magnetically active particles may be attached to the bone particlesusing silane chemistry or other coupling agents, for example zirconatesand titanates, or mixed into the polymer as part of the composite.Alternatively, or in addition, poly(ethylene glycol) (PEG) may beattached to the bone particles. Biologically active molecules, forexample, small molecules, bioactive agents, and biomolecules such aslipids may be linked to the bone particles through silane SAMs, using apolysialic acid linker (see, for example, U.S. Pat. No. 5,846,951) orwith m-maleimidobenzoyl-N-hydroxysuccinimide ester,beta-maleimidopropionic acid N-hydroxysuccinimide ester, or succinicanhydride. Equistar of Houston Tex. manufactures INTEGRATE™ resins,polyolefins that have been chemically modified to provide polaranhydride functionality on the polymer backbone. The polar functionalityallows these products to function as coupling agents in blends ofdissimilar materials, promote compatibility in polymer blends and toprovide improved bonding in adhesive formulations. Coupling agents maybe used between bone and the polymer component in order to enhancebonding at the bone/polymer interfaces of the composite. For example,silane groups may be incorporated into the polymer as a side chain or bymodifying the polymer after polymerization. The silane groups may thenbe attached to bone particles. Alternatively, coupling agents havingreactive end groups may be attached to the bone particles and thenreacted with the polymer.

Biologically active materials, including biomolecules, small molecules,and bioactive agents may also be combined with the polymer and bone to,for example, stimulate particular metabolic functions, recruit cells, orreduce inflammation. For example, nucleic acid vectors, includingplasmids and viral vectors, that will be introduced into the patient'scells and cause the production of growth factors such as bonemorphogenetic proteins may be included in the composite. RNAi,anti-sense RNA or other technologies may be used to reduce theproduction of various factors. These materials need not be covalentlybonded to either component of the composite. A material may beselectively distributed on or near the surface of the composite usingthe layering techniques described above. While the surface of thecomposite will be mixed somewhat as the composite is manipulated in theimplant site, the thickness of the surface layer will ensure that atleast a portion of the surface layer of the composite remains at thesurface of the implant. Alternatively or in addition, biologicallyactive components may be covalently linked to the bone particles beforecombination with the polymer. For example, silane coupling agents havingamine, carboxyl, hydroxyl, or mercapto groups may be attached to thebone particles through the silane and then to reactive groups on abiomolecule, small molecule, or bioactive agent.

The composite may also be seeded with cells. For example, a patient'sown cells may be harvested, expanded, and mixed with the composite.Alternatively, stem cells or exogenous cells may be employed. Exemplarycells for use with the invention include mesenchymal stem cells andconnective tissue cells, including osteoblasts, osteoclasts, andfibroblasts.

The collagen fibers exposed by demineralization are typically relativelychemically inert. The collagen may be rendered more reactive by frayingthe triple helical structure of the collagen to partially or fullyseparate the individual collagen strands from each other. Rinsing thepartially demineralized bone particles in an alkaline solution will fraythe collagen fibrils. For example, bone particles may be mixed withwater at a pH of about 10 for about 8 hours, after which the solution isneutralized. One skilled in the art will recognize that the pH, the timeperiod, or both may be adjusted to modify the extent of fraying.Agitation, for example, in an ultrasonic bath, may reduce the processingtime. Alternatively, the particles may be sonicated with water,surfactant, alcohol, or some combination of these. Both frayed andunfrayed collagen fibers may be derivatized with biomolecules, smallmolecules, bioactive molecules, biologically inactive compounds, or somecombination of these. These materials may be covalently ornon-covalently linked to the exposed collagen strands through reactiveamino acids on the collagen fiber such as lysine, arginine,hydroxylysine, proline, and hydroxyproline.

Implantation of the Composite

The composite may be implanted directly into a tissue site or formedinto a shape immediately prior to and/or for a period afterimplantation. Alternatively, or in addition, the shape of the compositemay be manipulated before, during, or for a period after implantation.The term “immediately prior” is used to indicate that the desired shapeis identified, the composite formed into the shape, and the shapedcomposite implanted into a patient as part of a surgical procedure.

Because the composite can be formed and manipulated in situ, a surgeondoes not need to know the exact size or shape of the implant site beforescheduling a procedure to fill it. In addition, the surgeon does notneed to schedule an additional procedure or prolong surgery to preparethe implant site before implantation. Rather, once the characteristicsof the implant site are known, the composite is shaped to match it.

In one embodiment, a series of molds of a particular bone or boneportion are available to a surgeon during surgery. After determining thedimensions of the implant site, the surgeon forms the composite in theappropriate mold, allows the composite to harden, and implants the newlyformed implant into the patient. As noted above, the composite may beproduced with the polymer in a softened state or softened by the userimmediately before forming. The user may then initiate setting of thecomposite after it is formed. In one embodiment, a surgeon opens apackage of formable composite and shapes it during surgery to the exactshape of the patient site.

In an alternative embodiment, the softened composite is formed in theimplant site. For example, a bony defect may be filled by the formablecomposite. The composite is pressed into the defect site to ensure thatit fills all the small spaces of the site. If the composite is softenedby the user for forming in the implant site, it is preferably softenedby heat or other energy, although a biocompatible solvent may be used aswell. In one embodiment, the polymer undergoes a conformational changeupon application of a particular wavelength of light to become formable.The polymer may simply relax over time to set or may set upon exposureto a different wavelength of light.

In embodiments where the polymer component becomes formable when heated,the heat absorbed by bone particles in the composite may increase thecooling time of the composite, extending the time available to form thecomposite into an implant. Depending on the relative heat capacities ofthe bone and the polymer components and the size of the bone particles,the bone may continue to release heat into the surrounding polymer afterthe time when the polymer alone would have cooled. The size and densitydistribution of bone particles within the composite may be optimized toadjust the amount of heat released into portions of an osteoimplantduring and after implantation.

The composite may be formed, machined, or both, into a variety ofshapes. Exemplary shapes include, without limitation, sheet, plate,particle, sphere, hemisphere strand, coiled strand, capillary network,film, fiber, mesh, disk, cone, portion of a cone, pin, screw, tube, cup,tooth, tooth root, strut, wedge, portion of wedge, cylinder, threadedcylinder, rod, hinge, rivet, anchor, spheroid, ellipsoid, oblatespheroid, prolate ellipsoid, or hyperbolic paraboloid. In oneembodiment, the composite is formed in a mold having the shape of adesired implant. For example, a mold may be shaped as a portion of abone or as a whole bone that is being replaced. Exemplary bones that maybe replaced using the techniques of the invention include ethmoid,frontal, nasal, occipital, parietal, temporal, mandible, maxilla,zygomatic, cervical vertebra, thoracic vertebra, lumbar vertebra,sacrum, rib, sternum, clavicle, scapula, humerus, radius, ulna, carpalbones, metacarpal bones, phalanges, incus, malleus, stapes, ilium,ischium, pubis, femur, tibia, fibula, patella, calcaneus, tarsal andmetatarsal bones. In another embodiment, the composite is formed as aplate or similar support, including but not limited to an I-shape to beplaced between teeth for intra-bony defects, a crescent apron for singlesite use, a rectangular bib for defects including both the buccal andlingual alveolar ridges, neutralization plates, spoon plates, condylarplates, clover leaf plates, compression plates, bridge plates, waveplates, etc. Partial tubular as well as flat plates may be fabricatedusing the composite of the invention. Alternatively, the composite maybe a block that is machined into a desired shape. The composite may bemachined in either its set condition or its formable condition. Suchmachining might be simpler for an end user, such as a surgeon, when thecomposite is in its formable condition.

If desired, mechanical fasteners such as screws, rivets, or sutures maybe used to improve the retention of the implant. In one embodiment, nodrilling is required to fix the fastener to the implant. Rather, thefastener is inserted into the composite while it is still pliable orwhile the polymer and the bone particles are being mixed. Of course, therigid composite may be drilled if desired. If the shape of the finalimplant is somehow incorrect, composites that are softened by heatingmay be reheated and the shape readjusted.

EXAMPLES

Polymer pellets of starch poly(caprolactone) were placed in a microwaveoven and heated to approximately 130° F. (54.4° C.). The pellets werethen pressed together by hand to form a larger mass of polymer. Beforethe polymer cooled, partially demineralized bovine bone particles werefolded into the polymer until the polymer contained approximately 50% byweight of bone particles. The composite was then heated and formed intothe desired final shape. Upon cooling to normal body temperature, thecomposite set to form a rigid construct in the desired shape. Thecomposite could be repeatedly heated and reshaped. Once formed, thecomposite was subjected to approximately 10 heating/cooling cycles withno observable degradation of handling or setting properties.

Other embodiments of the invention will be apparent to those skilled inthe art from a consideration of the specification or practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with the true scope and spiritof the invention being indicated by the following claims.

1. A composite osteoimplant, comprising: a polymer, wherein the polymeris selected from the group consisting of starch poly(caprolactone),poly(caprolactone), poly(l-lactide), poly(dl-lactide-co-glycolide),poly(l-lactide-co-dl-lactide), enantiomers of the above, co-polymers ofthe above, and mixtures of the above; and bone-derived particles;wherein the composite is formable during implantation or immediatelyprior to implantation and is settable under suitable conditions; andwherein the composite is not formable at about 37° C., and wherein thecomposite becomes formable when heated to a temperature greater thanabout 40° C.
 2. The osteoimplant of claim 1, wherein the compositebecomes formable when heated to a temperature greater than about 45° C.3. The osteoimplant of claim 2, wherein the composite becomes formablewhen heated to a temperature greater than about 50° C.
 4. Theosteoimplant of claim 3, wherein the composite becomes formable whenheated to a temperature greater than about 55° C.
 5. The osteoimplant ofclaim 4, wherein the composite becomes formable when heated to atemperature greater than about 60° C.
 6. The osteoimplant of claim 5,wherein the composite becomes formable when heated to a temperaturegreater than about 70° C.
 7. The osteoimplant of claim 6, wherein thecomposite becomes formable when heated to a temperature greater thanabout 80° C.
 8. The osteoimplant of claim 7, wherein the compositebecomes formable when heated to a temperature greater than about 90° C.9. The osteoimplant of claim 1, wherein the composite is set byincreasing the cross-link density of the polymer component.
 10. Theosteoimplant of claim 1, wherein the composite further comprises amonomer, the composite becoming set when the monomer is covalentlyincorporated into the polymer.
 11. The osteoimplant of claim 1, whereinthe composite further comprises at least one member selected from thegroup consisting of bone marrow, biomolecules, small molecules,bioactive agents, calcium phosphate, calcium carbonate, and cells. 12.The osteoimplant of claim 1, wherein the composite further comprises atleast one member of nucleic acid vectors, mesenchymal stem cells,osteoblasts, osteoclasts, and fibroblasts.
 13. The osteoimplant of claim12, wherein the nucleic acid vector, when introduced into a cell,increases the cell's production of bone morphogenetic proteins.
 14. Theosteoimplant of claim 1, wherein the osteoimplant is capable of beingirrigated following implantation without substantially changing itsshape.
 15. The osteoimplant of claim 1, wherein the bone-derivedparticles are selected from the group consisting of nondemineralizedbone particles, partially demineralized bone particles, superficiallydemineralized bone particles, fully demineralized bone particles andmixtures thereof.
 16. The osteoimplant of claim 1, wherein thebone-derived particles are obtained from a member of the groupconsisting of cortical bone, cancellous bone, cortico-cancellous bone,and mixtures thereof.
 17. The osteoimplant of claim 1, wherein thebone-derived particles are obtained from a member of the groupconsisting of autogenous bone, allogenic bone, xenogeneic bone,transgenic bone, and mixtures thereof.
 18. The osteoimplant of claim 1,wherein the bone-derived particles are about 10% to about 99% by weightof the composite.
 19. The osteoimplant of claim 18, wherein thebone-derived particles are about 25% to about 50% by weight of thecomposite.
 20. The osteoimplant of claim 1, wherein a surface of thebone-derived particles is modified with at least one member selectedfrom the group consisting of biomolecules, small molecules, bioactiveagents, non-biologically active materials, and any combination of theabove.
 21. The osteoimplant of claim 20, wherein the member is linked tothe surface by a coupling agent.
 22. The osteoimplant of claim 1,wherein at least a portion of the bone-derived particles are covalentlylinked to one another.
 23. The osteoimplant of claim 1, wherein collagenfibers at the surface of the bone-derived particles are exposed.
 24. Theosteoimplant of claim 23, wherein the exposed collagen fibers arepartially or fully separated from one another.
 25. The osteoimplant ofclaim 23, wherein the exposed collagen fibers are derivatized with amoiety selected from the group consisting of biomolecules, smallmolecules, bioactive agents, non-biologically active materials, and anycombination of the above.
 26. The osteoimplant of claim 1, wherein thepolymer comprises poly(caprolactone).
 27. The osteoimplant of claim 1,wherein the bone derived particles and the polymer are linked with acoupling agent.
 28. The osteoimplant of claim 1, wherein theosteoimplant has a shape selected from the group consisting of bone, asection of a bone, sheet, plate, particle, sphere, hemisphere strand,coiled strand, capillary network, film, fiber, mesh, disk, cone, portionof a cone, pin, screw, tube, cup, tooth, tooth root, strut, wedge,portion of wedge, cylinder, threaded cylinder, rod, hinge, rivet,anchor, spheroid, ellipsoid, oblate spheroid, prolate ellipsoid, andhyperbolic paraboloid.
 29. The osteoimplant of claim 1, wherein theosteoimplant comprises a plurality of pieces of composite, wherein thepieces are joined together.
 30. The osteoimplant of claim 29, whereinthe pieces are joined together with a member selected from the groupconsisting of adhesives, mechanical fasteners, ultrasonic bonding, andany combination of the above.
 31. The osteoimplant of claim 1, whereinthe composite is adapted and constructed to be formed in a mold.
 32. Theosteoimplant of claim 1, wherein the distribution of bone-derivedparticles within the composite is not uniform with respect to a memberof the group consisting of volume fraction, size, density, shape, sizedistribution, and any combination of the above.
 33. The osteoimplant ofclaim 1, wherein at least a portion of the bone-derived particles in thecomposite are elongate, and wherein an arrangement of bone-derivedparticles in the composite is isotropic or anisotropic.
 34. Theosteoimplant of claim 1, wherein at least a portion of the bone-derivedparticles in the composite are elongate, and wherein a relativealignment of bone-derived particles in a first portion of the compositeis different than the relative alignment of bone-derived particles in asecond portion of the composite.